Before Charlie goes to heaven, his pocket watch strap is red. When Charlie is on the dock right before he gets hit by the car, as Killer is trying to tie the blindfold on a singing Charlie, you see that Charlie's pocket watch strap is blue for that shot, then goes back to red the next.
When King Gator is swimming past Anne-Marie with Charlie on his belly, Charlie helps her up and she sits in his lap. Then when she tells him she doesn't feel good, she is sitting beside him. But from the rear view she is sitting on Charlie's lap again.
At the very end, when Annabelle (the pink whippet) is taking Charlie back up to Heaven, Charlie has his blue pocket-watch again (the one he lost in the lake) and their lips are moving yet, they aren't talking. This is because they re-used the beginning of the "Let Me Be Surprised" scene.
Despite Charlie being hit by a car pushed deliberately by Carface only the car is seen plunging into the water. This was probably due to the fact that seeing Charlie getting killed would be to dark for a kid's film.